<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div class="header" style="background-color: aquamarine;">
        头部区域
    </div>

    <div class="content">
        内容区域 
        <!-- span是行级标签 -->
        <span style="background-color: aqua;">a</span>
        <span>b</span>
        <span>c</span>
        <span>d</span>

    </div>

    <div class="footer">尾部区域</div>
</body>
</html>